Low- and high-density lipoproteins modulate function, apoptosis, and proliferation of primary human and murine pancreatic beta-cells

Protection against Glucolipotoxicity by High Density Lipoprotein in Human PANC-1 Hybrid 1.1B4 Pancreatic Beta Cells: The Role of microRNA

High-density lipoproteins provide protection against the damaging effects of glucolipotoxicity in beta cells, a factor which sustains insulin secretion and staves off onset of type 2 diabetes mellitus. This study examines epigenetic changes in small non-coding microRNA sequences induced by high density lipoproteins in a human hybrid beta cell model, and tests the impact of delivery of a single sequence in protecting against glucolipotoxicity. Human PANC-1.1B4 cells were used to establish Bmax and Kd for [³H]cholesterol efflux to high density lipoprotein, and minimum concentrations required to protect cell viability and reduce apoptosis to 30mM glucose and 0.25 mM palmitic acid. Microchip array identified the microRNA signature associated with high density lipoprotein treatment, and one sequence, hsa-miR-21-5p, modulated via delivery of a mimic and inhibitor. The results confirm that low concentrations of high-density lipoprotein can protect against glucolipotoxicity, and report the global microRNA profile associated with this lipoprotein; delivery of miR-21-5p mimic altered gene targets, similar to high density lipoprotein, but could not provide sufficient protection against glucolipotoxicity. We conclude that the complex profile of microRNA changes due to HDL treatment may be difficult to replicate using a single microRNA, findings which may inform current drug strategies focused on this approach.

Sphingosine 1-phosphate metabolism and insulin signaling

Insulin is the main anabolic hormone secreted by β-cells of the pancreas stimulating the assimilation and storage of glucose in muscle and fat cells. It modulates the postprandial balance of carbohydrates, lipids and proteins via enhancing lipogenesis, glycogen and protein synthesis and suppressing glucose generation and its release from the liver. Resistance to insulin is a severe metabolic disorder related to a diminished response of peripheral tissues to the insulin action and signaling. This leads to a disturbed glucose homeostasis that precedes the onset of type 2 diabetes (T2D), a disease reaching epidemic proportions. A large number of studies reported an association between elevated circulating fatty acids and the development of insulin resistance. The increased fatty acid lipid flux results in the accumulation of lipid droplets in a variety of tissues. However, lipid intermediates such as diacylglycerols and ceramides are also formed in response to elevated fatty acid levels. These bioactive lipids have been associated with the pathogenesis of insulin resistance. More recently, sphingosine 1-phosphate (S1P), another bioactive sphingolipid derivative, has also been shown to increase in T2D and obesity. Although many studies propose a protective role of S1P metabolism on insulin signaling in peripheral tissues, other studies suggest a causal role of S1P on insulin resistance. In this review, we critically summarize the current state of knowledge of S1P metabolism and its modulating role on insulin resistance. A particular emphasis is placed on S1P and insulin signaling in hepatocytes, skeletal muscle cells, adipocytes and pancreatic β-cells. In particular, modulation of receptors and enzymes that regulate S1P metabolism can be considered as a new therapeutic option for the treatment of insulin resistance and T2D.

APOA1: a Protein with Multiple Therapeutic Functions

PURPOSE OF THE REVIEW

Apolipoprotein (APO) A1, the main apolipoprotein of plasma high-density lipoproteins (HDLs), has several well documented cardioprotective functions. A number of additional potentially beneficial functions of APOA1 have recently been identified. This review is concerned with the therapeutic potential of all of these functions in multiple disease states.

RECENT FINDINGS

Knowledge of the beneficial functions of APOA1 in atherosclerosis, thrombosis, diabetes, cancer, and neurological disorders is increasing exponentially. These insights have led to the development of clinically relevant peptides and APOA1-containing, synthetic reconstituted HDL (rHDL) preparations that mimic the functions of full-length APOA1. APOA1 is a multifunctional apolipoprotein that has therapeutic potential in several diseases. Translation of this knowledge into the clinic is likely to be dependent on the efficacy and bioavailability of small peptides and synthetic rHDL preparations that are currently under investigation, or in development.

HDL (High-Density Lipoprotein) and ApoA-1 (Apolipoprotein A-1) Potentially Modulate Pancreatic α-Cell Glucagon Secretion

OBJECTIVE

Subjects with low levels of HDL (high-density lipoprotein) and ApoA-1 (apolipoprotein A-1) have increased risk to develop type 2 diabetes. HDL levels are an independent predictor of β-cell function and positively modulate it. Type 2 diabetes is characterized by defects in both β and α-cell function, but the effect of HDL and ApoA1 on α-cell function is unknown. Approach and Results: We observed a significant negative correlation (r=-0.422, P<0.0001) between HDL levels and fasting glucagon in a cohort of 132 Italian subjects. In a multivariable regression analysis including potential confounders such as age, sex, BMI, triglycerides, total cholesterol, fasting and 2-hour postload glucose, and fasting insulin, the association between HDL and fasting glucagon remained statistically significant (β=-0.318, P=0.006). CD1 mice treated with HDL or ApoA-1 for 3 consecutive days showed a 32% (P<0.001) and 23% (P<0.05) reduction, respectively, in glucagon levels following insulin-induced hypoglycemia, compared with controls. Treatment of pancreatic αTC1 clone 6 cells with HDL or ApoA-1 for 24 hours resulted in a significant reduction of glucagon expression (P<0.04) and secretion (P<0.01) after an hypoglycemic stimulus and increased Akt (RAC-alpha serine/threonine-protein kinase) and FoxO1 (forkhead/winged helix box gene, group O-1) phosphorylation. Pretreatment with Akt inhibitor VIII, PI3K (phosphatidylinositol 3-kinase) inhibitor LY294002, and HDL receptor SCARB-1 (scavenger receptor class B type 1) inhibitor BLT-1 (block lipid transport-1) restored αTC1 cell response to low glucose levels.

CONCLUSIONS

These results support the notion that HDL and ApoA-1 modulate glucagon expression and secretion by binding their cognate receptor SCARB-1, and activating the PI3K/Akt/FoxO1 signaling cascade in an in vitro α-cell model. Overall, these results raise the hypothesis that HDL and ApoA-1 may have a role in modulating glucagon secretion.

Early postpartum dyslipidemia and its potential predictors during pregnancy in women with a history of gestational diabetes mellitus

BACKGROUND

This study aimed to analyze the incidence of early postpartum dyslipidemia and its potential predictors in women with a history of gestational diabetes mellitus (GDM).

METHODS

This was a retrospective study. Five hundred eighty-nine women diagnosed with GDM were enrolled and followed up at 6-12 weeks after delivery. A 75 g oral glucose tolerance test (OGTT) and lipid levels were performed during mid-trimester and the early postpartum period. Participants were divided into the normal lipid group and dyslipidemia group according to postpartum lipid levels. Demographic and metabolic parameters were analyzed. Multiple logistic regression was performed to analyze the potential predictors for early postpartum dyslipidemia. A receiver operating characteristic curve (ROC) was calculated to determine the cut-off values.

RESULTS

A total of 38.5% of the 589 women developed dyslipidemia in early postpartum and 60% of them had normal glucose metabolism. Delivery age, systolic blood pressure (SBP), glycated hemoglobin (HbA1c) and low-density lipoprotein cholesterol (LDL-C) were independent predictors of early postpartum dyslipidemia in women with a history of GDM. The cut-offs of maternal age, SBP, HbA1c values, and LDL-C levels were 35 years, 123 mmHg, 5.1%, and 3.56 mmol/L, respectively. LDL-C achieved a balanced mix of high sensitivity (63.9%) and specificity (69.2%), with the highest area under the receiver operating characteristic curve (AUC) (0.696). When LDL-C was combined with age, SBP, and HbA1c, the AUC reached to 0.733.

CONCLUSIONS

A lipid metabolism evaluation should be recommended in women with a history of GDM after delivery, particularly those with a maternal age > 35 years, SBP > 123 mmHg before labor, HbA1c value > 5.1%, or LDL-C levels > 3.56 mmol/L in the second trimester of pregnancy.

Sphingosine-1-Phosphate Metabolism in the Regulation of Obesity/Type 2 Diabetes

Obesity is a pathophysiological condition where excess free fatty acids (FFA) target and promote the dysfunctioning of insulin sensitive tissues and of pancreatic β cells. This leads to the dysregulation of glucose homeostasis, which culminates in the onset of type 2 diabetes (T2D). FFA, which accumulate in these tissues, are metabolized as lipid derivatives such as ceramide, and the ectopic accumulation of the latter has been shown to lead to lipotoxicity. Ceramide is an active lipid that inhibits the insulin signaling pathway as well as inducing pancreatic β cell death. In mammals, ceramide is a key lipid intermediate for sphingolipid metabolism as is sphingosine-1-phosphate (S1P). S1P levels have also been associated with the development of obesity and T2D. In this review, the current knowledge on S1P metabolism in regulating insulin signaling in pancreatic β cell fate and in the regulation of feeding by the hypothalamus in the context of obesity and T2D is summarized. It demonstrates that S1P can display opposite effects on insulin sensitive tissues and pancreatic β cells, which depends on its origin or its degradation pathway.

Low-density lipoprotein cholesterol : high-density lipoprotein cholesterol ratio is associated with incident diabetes in Chinese adults: A retrospective cohort study

Aims/Introduction

Dyslipidemia plays a critical role in the pathogenesis of metabolic syndrome and diabetes. Evidence has increasingly shown that the ratio of low‐ to high‐density lipoprotein cholesterol (LDL‐C/HDL‐C) is a novel marker for increased risk of insulin resistance and cardiovascular diseases. However, the correlation between the LDL‐C/HDL‐C ratio and diabetes risk is rarely reported. This is the first study to investigate the association between the LDL‐C/HDL‐C ratio and new‐onset diabetes in a large community‐based cohort.

Materials and Methods

In this retrospective cohort study, a total of 116,661 adults without baseline diabetes were enrolled. Participants were stratified into four groups based on LDL‐C/HDL‐C ratio quartiles. The outcome of interest was new‐onset diabetes.

Results

During a median follow‐up period of 2.98 years, 2,681 (2.3%) new diabetes cases were recorded. The total cumulative incidence of diabetes progressively increased alongside LDL‐C/HDL‐C ratio quartiles (0.31, 0.43, 0.68 and 0.88%, respectively, P‐value for trend <0.001). After adjusting for potential confounders, using the lowest quartile of the LDL‐C/HDL‐C ratio as the reference, the risk of diabetes increased with LDL‐C/HDL‐C ratio quartiles (P‐value for trend <0.001); in particular, from the second to fourth quartile, hazard ratios were 1.18 (95% confidence interval 0.87–1.59), 1.42 (95% confidence interval 1.07–1.90) and 1.92 (95% confidence interval 1.43–2.59), respectively. The results were also robust to challenges in multiple sensitivity analyses.

Conclusions

Among the Chinese population, elevated LDL‐C/HDL‐C ratio might be an independent risk factor for new‐onset diabetes.

Lipid efflux mechanisms, relation to disease and potential therapeutic aspects

Lipids are hydrophobic and amphiphilic molecules involved in diverse functions such as membrane structure, energy metabolism, immunity, and signaling. However, altered intra-cellular lipid levels or composition can lead to metabolic and inflammatory dysfunction, as well as lipotoxicity. Thus, intra-cellular lipid homeostasis is tightly regulated by multiple mechanisms. Since most peripheral cells do not catabolize cholesterol, efflux (extra-cellular transport) of cholesterol is vital for lipid homeostasis. Defective efflux contributes to atherosclerotic plaque development, impaired β-cell insulin secretion, and neuropathology. Of these, defective lipid efflux in macrophages in the arterial walls leading to foam cell and atherosclerotic plaque formation has been the most well studied, likely because a leading global cause of death is cardiovascular disease. Circulating high density lipoprotein particles play critical roles as acceptors of effluxed cellular lipids, suggesting their importance in disease etiology. We review here mechanisms and pathways that modulate lipid efflux, the role of lipid efflux in disease etiology, and therapeutic options aimed at modulating this critical process.

Association between lipids and apolipoproteins on type 2 diabetes risk; moderating effects of gender and polymorphisms; the ATTICA study

BACKGROUND AND AIMS

Type 2 diabetes mellitus (T2DM) is a condition defined by hyperglycaemia, but also often presents with dyslipidaemia and suppressed HDL cholesterol. Mendelian randomization studies have suggested a causal link between low HDL cholesterol and T2DM. However, influences of gender, polymorphisms and lifestyle, all known to influence HDL cholesterol, have not been fully explored in a prospective cohort.

METHODS AND RESULTS

In 2001-2002, a random sample of 1514 males (18-87 years old) and 1528 females (18-89 years old) were recruited in the ATTICA study. The 10-year follow-up (2011-2012) included 1485 participants. Lipids and lipoproteins levels, glucose and insulin levels were measured together with apolipoprotein A1 (apoA1) 75 G/A genotype, which is known to influence HDL-cholesterol. In total, 12.9% of the study sample developed T2DM within the 10-year follow-up period. In multivariable models, for each mg/dL increase in apoA1 levels in males, 10-year T2DM risk decreased 1.02%; while every unit increase in apoB/LDL-cholesterol ratio increased risk 4-fold. Finally, for every unit increase in triglycerides/apoA1 ratio, the risk increased 85%. HOMA-IR independently predicted T2DM 10-year incidence only for carriers of GG polymorphism (all, p < 0.05), but not in carriers of the GA polymorphism (all, p > 0.05).

CONCLUSION

ApoA1 was associated with decreased T2DM risk and TG/ApoA1 and apoB/LDL were associated with increased risk of T2DM, only in males. ApoA1 polymorphism, which is associated with lower HDL cholesterol, influenced the predictive effects of HOMA-IR on T2DM incidence, which appeared to be moderated by physical activity, suggesting potential scope for more targeted preventative strategies.

HDL cholesterol is an independent predictor of β-cell function decline and incident type 2 diabetes: A longitudinal study

BACKGROUND

Experimental evidence indicates that high-density lipoprotein (HDL) may stimulate glucose uptake and improve β-cell function. The aim of this study was to evaluate whether lower levels of HDL may affect the risk to develop type 2 diabetes.

METHODS

Incident rate of type 2 diabetes and changes in insulin sensitivity and β-cell function over 5.5-year follow-up were examined in 670 non-diabetic subjects stratified in tertiles according to basal HDL levels.

RESULTS

As compared to the highest tertile of HDL, individuals with lower levels of HDL have an increased risk to develop type 2 diabetes independently from several cardiometabolic risk factors (odds ratio: 2.88, 95% confidence interval: 1.05-7.91), and exhibited a greater deterioration of β-cell function, estimated by the disposition index, over 5.5-year follow-up. Conversely, changes in Matsuda index of insulin sensitivity over the follow-up were not significantly different amongst the three HDL groups. In a multivariable regression analysis model including age, sex, waist circumference, triglycerides, total cholesterol, C-reactive protein, fasting and 2-hour post-load glucose, family history of type 2 diabetes and smoking habit, HDL concentration at baseline was an independent predictor of β-cell function decline over the follow-up (β = .30, P = .0001). Mediation analysis showed that the association between lower HDL levels at baseline and increased risk of incident diabetes was mediated by β-cell function deterioration during the follow-up (t = -3.32, P = .001).

CONCLUSIONS

Subjects with lower levels of HDL have an increased risk to develop type 2 diabetes likely due to a greater β-cell function decline over time.

High-Density Lipoproteins and Apolipoprotein A1

High-density lipoprotein (HDL) and its main protein component apolipoprotein (apo)A-I, play an important role in cholesterol homeostasis. It has been demonstrated that HDLs comprise of a very heterogeneous group of particles, not only regarding size but also composition. HDL's best described function is its role in the reverse cholesterol transport, where lipid-free apoA-I or small HDLs can accept and take up cholesterol from peripheral cells and subsequently transport this to the liver for excretion. However, several other functions have also been described, like anti-oxidant, anti-inflammatory and anti-thrombotic effects. In this article, the general features, synthesis and metabolism of apoA-I and HDLs will be discussed. Additionally, an overview of HDL functions will be given, especially in the context of some major pathologies like cardiovascular disease, cancer and diabetes mellitus. Finally, the therapeutic potential of raising HDL will be discussed, focussing on the difficulties of the past and the promises of the future.

LDL, LDL receptors, and PCSK9 as modulators of the risk for type 2 diabetes: a focus on white adipose tissue

Type 2 diabetes (T2D) and cardiovascular disease (CVD) share many risk factors such as obesity, unhealthy lifestyle, and metabolic syndrome, whose accumulation over years leads to disease onset. However, while lowering plasma low-density lipoprotein cholesterol (LDLC) is cardio-protective, novel evidence have recognised a role for common LDLC-lowering variants (e.g. in HMGCR, PCSK9, and LDLR) and widely used hypocholesterolemic drugs that mimic the effects of some of these variants (statins) in higher risk for T2D. As these conditions decrease plasma LDLC by increasing tissue-uptake of LDL, a role for LDL receptor (LDLR) pathway was proposed. While underlying mechanisms remain to be fully elucidated, work from our lab reported that native LDL directly provoke the dysfunction of human white adipose tissue (WAT) and the activation of WAT NLRP3 (Nucleotide-binding domain and Leucine-rich repeat Receptor, containing a Pyrin domain 3) inflammasome, which play a major role in the etiology of T2D. However, while elevated plasma numbers of apolipoprotein B (apoB)-containing lipoproteins (measured as apoB, mostly as LDL) is associated with WAT dysfunction and related risk factors for T2D in our cohort, this relation was strengthened in regression analysis by lower plasma proprotein convertase subtilisin/kexin type 9 (PCSK9). This supports a central role for upregulated pathway of LDLR and/or other receptors regulated by PCSK9 such as cluster of differentiation 36 (CD36) in LDL-induced anomalies. Targeting receptor-mediated uptake of LDL into WAT may reduce WAT inflammation, WAT dysfunction, and related risk for T2D without increasing the risk for CVD.

Genotyping and Frequency of PCSK9 Variations Among Hypercholesterolemic and Diabetic Subjects

Non-synonymous single-nucleotide polymorphism (SNPs) in the gene for proprotein convertase subtilisin/kexin type 9 (PCSK9) can influence cholesterol and glucose metabolism, leading to increased risk of cardiovascular disease and diabetes. To determine the frequency of four common PCSK9 SNPs, L10Ins, A56V, I474V, and E670G, in a population sample (n = 98) of the Hail region of Kingdom of Saudi Arabia. Blood was collected from participants; serum cholesterol, blood glucose and glycated hemoglobin were determined; genomic DNA was extracted and PCR amplicons from SNP-containing PCSK9 exons were subjected to Sanger sequencing. Out of 98 participants. 10 (10.20%) carried none of the SNPs, 2 (2.04%) the L10ins/A56V linked SNPs, 35 (35.71%) the I474V SNP, 22 (22.45%) both the I474V and E670G SNPs, and 29 (29.59%) the E670G SNP. Of the 30 eucholesterolemic diabetics patients, 11 (36.66%) carried the I474V SNP, 10 (33.33%) the E679G SNP and 6 (20%) the I474V/E679G. SNPs. Of 63 diabetic patients, 26 (41.26%) carry I474V SNP and 22 (34.92%) carry E670G SNP. Our data demonstrated that the I474V and E670G PCSK9 variants are very frequent in the Hail region of Saudi Arabia and are found at even higher frequency among diabetics. Further investigations are needed to determine whether these variations or another variant segregating with them can explain its apparent association with diabetes in this population.

Sphingolipid metabolism in type 2 diabetes and associated cardiovascular complications

Sphingolipid metabolism is dysregulated in type 2 diabetes mellitus (T2DM); however, the focus of previous studies was mostly limited to ceramide (Cer), and only few studies have investigated other metabolites, including sphingosine-1 phosphate (So1P). The present study aimed to examine the involvement of 8 major sphingolipid metabolites, including Cer, glucosyl ceramide (GluCer), lactosyl ceramide (LacCer), sphingomyelin (SM), sphinganine (Sa), So1P, sphingosine (So) and sphinganine-1-phosphate (Sa1P), during the progression of T2DM, and to evaluate the ability of serum sphingolipids to predict cases of diabetes with an elevated risk of cardiovascular complications. Blood samples were obtained from 245 participants who were divided into 3 groups: Healthy controls, pre-diabetes (pre-DM) and diagnosed diabetes. The 8 major sphingolipid metabolites were measured by high-performance liquid chromatography-tandem mass spectrometry and blood parameters were determined by routine laboratory assays for all subjects. Among the sphingolipid metabolites, So1P was associated with sex and lean mass index, but not with the body mass index. So1P was highest in healthy controls and gradually decreased when the disease proceeded to pre-DM and T2DM. GluCer, SM, Sa and So decreased in pre-DM and rose again in T2DM, graphically exhibiting a 'U' shape change during the progression of diabetes. So1P and Sa were identified to be significantly associated with cardiovascular complications by multivariate logistic regression analysis. Receiver operating characteristic curve analysis also suggested that So1P and Sa were able to indicate cardiovascular complications in diabetic patients. Pre-DM and diabetes were significantly associated with decreased So1P, SM, Sa and So, compared with the healthy controls. So1P was correlated with the progression of T2DM, and was a predictor of an elevated risk of cardiovascular complications among T2DM patients, along with Sa. The present study was registered with ClinicalTrials.gov (no. NCT02826759; April 2016).

Treat-to-target HbA1c and lipid profile to prolong β-cell mass/function and optimize treatment goal attainment

BACKGROUND

To evaluate the relation between different serum lipid fractions and other known barriers to attain the HbA_1c  ≤ 7.0% (53 mmol/mol) target.

METHODS

Data on 2719 patients with type 2 diabetes were collected from the five waves of the International Diabetes Mellitus Practice Study implemented in Argentina (2006 to 2012) including demographic/socioeconomic profile, clinical, metabolic (HbA_1c and serum lipids) data, and treatment type and also, percentage of treatment goal attainment. Descriptive statistical analyses included ANOVA, χ² test, and Fisher exact test and univariate and multivariate logistic regression analyses, which identified predictive factors for HbA_1c  ≤ 7% (53 mmol/mol).

RESULTS

The average age was 63 years, primary/secondary education, health insurance, 10-year type 2 diabetes duration, most associated with cardiovascular risk factors and some microvascular/macrovascular complications; 94.5% received antihyperglycaemic drugs. Percentage of people on target: HbA_1c 51.2%, blood pressure 23.5%, total cholesterol 62.6%, low-density lipoprotein (LDL) cholesterol 38.9%, and triglycerides 61.1%. HbA_1c on target depended markedly on treatment type: more of those treated with lifestyle changes and significantly fewer of those receiving insulin. Only 4.1% had all parameters simultaneously on target. Multivariate logistic regression analyses showed that achieving HbA_1c  ≤ 7.0% (53 mmol/mol) was associated with higher educational level, shorter diabetes duration, and having reached goals for LDL cholesterol and triglycerides, whereas opposite results were obtained with insulin treatment and longer diabetes duration.

CONCLUSIONS

High LDL cholesterol and triglyceride levels simultaneously potentiate development/progression of chronic complications, exerting this effect in the long term by decreasing β-cell mass/function, thereby making it more difficult to reach HbA_1c values able to prevent complications.

The PI3K/Akt pathway is not a main driver in HDL-mediated cell protection

High-density lipoproteins (HDLs) can protect cells against a variety of death-inducing stresses. This is often accompanied by activation of the anti-apoptotic Akt kinase but whether this activation mediates the protective functions of HDLs is still unclear. In this study, we evaluated the roles of PI3K/Akt signaling in endoplasmic reticulum (ER) stress- and starvation-induced cell death using pharmacological and genetic approaches to gain a better understanding of the relationship between Akt- and HDL-mediated protection. Three cell models were used for this purpose, a primary endothelial cell line, an insulinoma cell line and a colon adenocarcinoma cell line. Our results show that HDLs indeed elicited mild Akt activation in all the tested cellular models. PI3K is one of the main upstream proteins involved in Akt stimulation. In the three cellular models, LY294002, a PI3K inhibitor, only slightly blunted HDLs protection, indicating that HDLs induce PI3K-independent cell protection. Furthermore, genetic ablation or silencing of Akt did not abolish the protective effects of HDLs. This study demonstrates that the PI3K-Akt signaling pathway is not the main mediator of the cell protective functions of HDLs. Further investigation is therefore needed to identify the intrinsic mechanism of HDL-mediated cell protection.

Apolipoprotein C-III and its defined lipoprotein subspecies in relation to incident diabetes: the Multi-Ethnic Study of Atherosclerosis

AIMS/HYPOTHESIS

Apolipoprotein C-III (apoC-III) is a small proinflammatory protein that may play a key role in diabetes pathophysiology. However, prior observational studies have been limited to predominantly white populations, and the biological links between apoC-III and diabetes, particularly the role of apoC-III on specific lipoprotein particles, are not yet well understood. We therefore investigated associations of total apoC-III and apoC-III-defined lipoprotein subspecies with incident diabetes and glucose metabolism measures in a multi-ethnic cohort.

METHODS

For the current analyses, baseline (2000-2002) plasma total apoC-III and apolipoprotein A-I concentrations of HDL containing or lacking apoC-III were newly measured via sandwich ELISA in 4579 participants from the Multi-Ethnic Study of Atherosclerosis. Multivariable Cox regression was used to examine associations of apolipoproteins with incident diabetes until early 2012 (567 cases), and linear mixed models were used to estimate associations with longitudinally assessed continuous measures of glucose metabolism. Similar exploratory analyses of plasma apolipoprotein B concentrations of LDL and VLDL containing or lacking apoC-III were performed in a subset of participants (LDL, n = 1545; VLDL, n = 1526).

RESULTS

In the overall population, elevated total apoC-III concentrations were associated with a higher rate of diabetes (top vs bottom quintile, HR 1.88; 95% CI 1.42, 2.47; p_trend = 0.0002). ApoC-III-defined HDL subspecies displayed opposing associations with incidence of diabetes (p for heterogeneity = 0.02). While HDL lacking apoC-III was inversely associated with incidence of diabetes (top vs bottom quintile, HR 0.66; 95% CI 0.46, 0.93; p_trend = 0.002), HDL containing apoC-III was not associated (HR 1.11; 95% CI 0.78, 1.58; p_trend = 0.61). Similarly, only HDL lacking apoC-III was beneficially associated with plasma glucose (p_trend = 0.003), HbA_1c (p_trend = 0.04) and insulin sensitivity (p_trend < 0.0001), and higher HDL containing apoC-III was associated with lower insulin sensitivity (p_trend = 0.04). Neither of the apoC-III-defined LDL subspecies was associated with incident diabetes, while VLDL was more strongly associated with the incidence of diabetes when it lacked apoC-III. Further adjustment for plasma triacylglycerols as a potential intermediate attenuated the associations of total apoC-III and apoC-III-defined lipoprotein subspecies. No statistically significant differences were observed across racial/ethnic groups.

CONCLUSIONS/INTERPRETATION

Our findings in a multi-ethnic population support the involvement of apoC-III in the development of diabetes, potentially through its association with circulating triacylglycerols. The presence of apoC-III on HDL also diminished the protective association of HDL with incident diabetes. Further investigation of apoC-III and apoC-III-defined HDL subspecies may inform the development of novel diabetes treatment and prevention strategies.

[Antidiabetic role of high density lipoproteins]

Disturbance in lipid metabolism can be both a cause and a consequence of the development of diabetes mellitus (DM). One of the most informative indicator of lipid metabolism is the ratio of atherogenic and antiatherogenic fractions of lipoproteins and their protein components. The review summarizes literature data and own results indicating the important role of high-density lipoprotein (HDL) and their main protein component, apolipoprotein A-I (apoA-I), in the pathogenesis of type 2 DM. On the one hand, HDL are involved in the regulation of insulin secretion by b-cells and insulin-independent absorption of glucose. On the other hand, insulin resistance and hyperglycemia lead to a decrease in HDL levels and cause modification of their protein component. In addition, HDL, possessing anti-inflammatory and mitogenic properties, provide anti-diabetic protection through systemic mechanisms. Thus, maintaining a high concentration of HDL and apoA-I in blood plasma and preventing their modification are important issues in the context of prevention and treatment of diabetes.

ATP-binding cassette sub-family a member1 gene mutation improves lipid metabolic abnormalities in diabetes mellitus

Background

Patients with diabetes mellitus were often accompanied with hyperlipidemia. ATP-binding cassette sub-family A member1 (ABCA1) promotes the efflux of lipids and thereby mediates the metabolism of cholesterol. The aim of our study was to determine the associations of ABCA1 gene polymorphisms with the risks of diabetes mellitus and dyslipidemia in diabetic patients.

Methods

We retrieved literature about the relationship between ABCA1 gene polymorphisms (C69T and R230C) and the risk of diabetes through PubMed, Web of Science, EMBASE, Wanfang Database, China National Knowledge Infrastructure (CNKI) and Cochrane database. Weighted mean difference (WMD) and odds ratio (OR) were used to compare continuous and dichotomous variables, respectively, accompanied by their 95% confidence interval (CI).

Results

A total of 1746 diabetic patients and 1292 non-diabetic controls were enrolled. All subjects were Caucasians. ABCA1 R230C T allele was significantly associated with reduced the risk of diabetes (OR = 0.75, 95% CI = 0.57–0.98, P = 0.04). There was no association of ABCA1 C69T gene polymorphisms with the risk of diabetes. However, subgroup analyses showed that the ABCA1 C69T gene mutation significantly reduced the risk of hypertriglyceridemia in diabetic patients as compared with that in non-diabetic subjects (dominant model: WMD =0.66, 95% CI = 0.52–0.8, P < 0.0001; recessive model: WMD = 0.47, 95%CI = 0.11–0.83, P = 0.01).

Conclusions

ABCA1 R230C T allele gene mutation is a protective in decreasing the risk of diabetes in Caucasians and ABCA1 C69T gene mutation markedly influences the level of lipid metabolism in diabetic patients.

Electronic supplementary material

The online version of this article (10.1186/s12944-019-0998-3) contains supplementary material, which is available to authorized users.

Vitamin D effects on sphingosine 1-phosphate signaling and metabolism in monocytes from type 2 diabetes patients and controls

Elevated sphingosine 1-phopshate (S1P) concentration was observed in type 2 diabetes mellitus (T2D). On the other side, 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) can influence the formation of sphingosine 1-phopshate (S1P) and the expression of S1P receptors, which are known to be involved in T2D. In order to evaluate mechanisms for the antiinflammatory potential of 1,25(OH)₂D₃, we investigated whether 1,25(OH)₂D₃ alters S1P signaling and metabolism in human CD14⁺ monocytes. Primary monocytes isolated from healthy controls (HC) and T2D patients were treated for 24 h with 10 nM 1,25(OH)₂D₃ in the absence or presence of 500 IU/ml interleukin-(IL)-1β. Thereafter, sphingosine kinase (SPHK)1, SPHK2 and S1P receptor 1-5 (S1P_1-5) mRNA expression levels were measured by TaqMan^™ analyses. Sphingolipid levels in cell supernatant were determined by high-performance liquid chromatography/tandem mass spectrometry (LC-MS/MS). 1,25(OH)₂D₃ treatment downregulated S1P₁ and S1P₂ mRNA expression compared to untreated monocytes of HC and T2D patients. In contrast, SPHK1, S1P₃ and S1P₄ mRNA expression levels were upregulated by 1,25(OH)₂D₃ treatment compared to the respective controls. Furthermore, reduced S1P₂ and increased S1P₃ and S1P₄ mRNA expression levels upon treatment with 1,25(OH)₂D₃ occurred in the presence of IL-1β. Additionally, S1P levels in cell supernatants were decreased in monocytes from HC and T2D patients by 1,25(OH)₂D₃ with or without IL-1β costimulation. The levels of sphingosine in cell supernatants were not influenced by 1,25(OH)₂D_3. Overall, our results demonstrate for the first time that 1,25(OH)₂D₃ treatment can influence S1P receptor and SPHK expression and S1P levels in primary monocytes of both HC and subjects with T2D. These findings justify further investigations into the sphingolipid metabolism and potential benefits of vitamin D treatment in diabetes.

Dyslipidemia: The untreated metabolic dysfunction in people with type 2 diabetes in Latin America. ARETAEUS study outcomes

Objective

To assess oral antihyperglycemic agents (OAHA) and/or statin treatment initiation in patients with type 2 diabetes (T2D) and time from diagnosis to both types of treatment initiation and intensification.

Research design and methods

We reviewed 662 retrospective medical records of patients with T2D diagnosed by 31 general practitioner or specialist sites across Mexico, Argentina, and Brazil. Demographic and clinical information was abstracted from patients’ medical records and summarized using descriptive statistics. Between-group differences were assessed with Student’s t-test for continuous variables and Fisher’s exact test for categorical variables. The starting time of each therapy (OAHA and statins, separately) was assessed using Kaplan-Meier estimates.

Results

At diagnosis, patients’ mean age was 53 years; 44% had hypertension, 42% were obese, and 23% had dyslipidemia. During the 2-year follow-up, 95% of patients received OAHAs but only 29% of those eligible for statins received this prescription. Mean ± SD and median (Q1, Q3) time to first OAHA was 59 ± 141 days and 1 (1, 31) day, respectively, and 230 ± 232 days and 132 (30, 406) days, respectively, for a statin. During follow-up, 51–53% of patients with HbA1c/FPG values above target did not intensify hyperglycemia treatment.

Conclusion

Dyslipidemia treatment in patients with T2D was delayed despite its known deleterious effect on atherosclerosis development and β-cell mass/function. Anti-hyperglycemic treatment was not intensified when targets were not attained. This prescriptive inertia needs to be corrected because attainment of HbA1c treatment goals becomes more difficult, favoring the development of diabetes complications.

Epigenetics and Sphingolipid Metabolism in Health and Disease

Sphingolipids represent one of the major classes of bioactive lipids. Studies of sphingolipids have intensified in the past several years, revealing their roles in nearly all cell biological processes. In addition, epigenetic regulation has gained substantial interest due to its role in controlling gene expression and activity without changing the genetic code. In this review, we first introduce a brief background on sphingolipid biology, highlighting its role in pathophysiology. We then illustrate the concept of epigenetic regulation, focusing on how it affects the metabolism of sphingolipids. We further discuss the roles of bioactive sphingolipids as epigenetic regulators themselves. Overall, a better understanding of the relationship between epigenetics and sphingolipid metabolism may help to improve the development of sphingolipid-targeted therapeutics.

Contribution and interaction of the low-density lipoprotein cholesterol to high-density lipoprotein cholesterol ratio and triglyceride to diabetes in hypertensive patients: A cross-sectional study

AIMS/INTRODUCTION

Hypertension is one of the most significant risk factors for diabetes. The present study aimed to investigate the associations of lipid profiles, including the ratio of low-density lipoprotein cholesterol (LDL-C)-to-high-density lipoprotein cholesterol (HDL-C) and triglyceride (TG) levels, as well as their interactions, with type 2 diabetes in hypertensive patients.

MATERIALS AND METHODS

Hypertensive patients without a history of diabetes and hypolipidemic agents were enrolled continuously at the Hypertension Clinic, Zhongshan Hospital, Fudan University (Shanghai, China) from 2014 to 2016. General clinical data, including body mass index, blood pressure, fasting glucose and 2-h post-load glucose levels, and lipid profiles, were collected. The LDL-C/HDL-C ratio, TG/HDL-C ratio and TC/HDL-C ratio were separately calculated. Statistical analyses were carried out by using SPSS software (version 13.0).

RESULTS

In total, 935 hypertensive patients were included, of which 114 patients (12.2%) were diagnosed with diabetes. After multivariate adjustments, the LDL-C/HDL-C ratio and TG levels had the most significant and independent associations with diabetes. In the multivariate logistic regression, the LDL-C/HDL-C ratio and TG were independently associated with diabetes. After the interaction variable was included, the LDL-C/HDL-C ratio remained independently associated with diabetes, but TG was replaced by TG*LDL-C/HDL-C.

CONCLUSIONS

In conclusion, elevated LDL-C/HDL-C ratios and TG levels were associated with diabetes in patients with hypertension, with an interactive effect of the LDL-C/HDL-C ratio and TG on diabetes in the hypertensive population.

Inhibiting PCSK9 - biology beyond LDL control

Clinical trials have unequivocally shown that inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) efficaciously and safely prevents cardiovascular events by lowering levels of LDL cholesterol. PCSK9 in the circulation is derived mainly from the liver, but the protein is also expressed in the pancreas, the kidney, the intestine and the central nervous system. Although PCSK9 modulates cholesterol metabolism by regulating LDL receptor expression in the liver, in vitro and in vivo studies have suggested that PCSK9 is involved in various other physiological processes. Although therapeutic PCSK9 inhibition could theoretically have undesired effects by interfering with these non-cholesterol-related processes, studies of individuals with genetically determined reduced PCSK9 function and clinical trials of PCSK9 inhibitors have not revealed clinically meaningful adverse consequences of almost completely eradicating PCSK9 from the circulation. The clinical implications of PCSK9 functions beyond lipid metabolism in terms of wanted or unwanted effects of therapeutic PCSK9 inhibition therefore appear to be limited. The objective of this Review is to describe the physiological role of PCSK9 beyond the LDL receptor to provide a rational basis for monitoring the effects of PCSK9 inhibition as these drugs gain traction in the clinic.

Phenotypical heterogeneity in responder and nonresponder male ApoE*3Leiden.CETP mice

The metabolic syndrome (MetS) is a major health issue worldwide and is associated with obesity, insulin resistance, and hypercholesterolemia. Several animal models were used to describe the MetS; however, many of them do not mimic well the MetS pathophysiology in humans. The ApoE*3Leiden.CETP mouse model overcomes part of this limitation, since they have a humanised lipoprotein metabolism and a heterogeneous response to MetS, similar to humans. The reported heterogeneity among them and their common classification refer to responder (R) and nonresponder (NR) mice; R mice show increased body weight, cholesterol, and triglycerides levels, whereas NR mice do not show this expected phenotype when fed a Western type diet. To define better the differences between R and NR mice, we focused on feeding behavior, body weight gain, glucose tolerance, and lipid parameters, and on an extensive pathological examination along with liver histology analysis. Our data confirmed that R mice resemble the pathological features of the human MetS: obesity, dysplipidemia, and glucose intolerance. NR mice do not develop the full dysmetabolic phenotype because of a severe inflammatory hepatic condition, which may heavily affect liver function. We conclude that R and NR mice are metabolically different and that NR mice have indications of severely impaired liver function. Hence, it is critical to identify and separate the respective mice to decrease data heterogeneity. Clinical chemistry and histological analysis should be used to confirm retrospectively the animals' classification. Moreover, we point out that NR mice may not be an appropriate control for studies involving ApoE*3Leiden.CETP R mice. NEW & NOTEWORTHY When compared with some other animal models, ApoE*3Leiden.CETP mice are better models to describe the metabolic syndrome. However, there is phenotypic heterogeneity between "responder" and "nonresponder" mice, the latter showing some evidence of hepatic pathology. A full phenotypic characterization and eventually postmortem analysis of the liver are warranted.

CETP inhibition, statins and diabetes

Type 2 diabetes is a causal risk factor for the development of atherosclerotic cardiovascular disease (ASCVD). While treatment with a statin reduces the risk of having an ASCVD event in all people, including those with type-2 diabetes, statin treatment also increases the likelihood of new onset diabetes when given to those with risk factors for developing diabetes. Treatment with the cholesteryl ester transfer protein (CETP) inhibitor, anacetrapib, reduces the risk of having a coronary event over and above that achieved with a statin. However, unlike statins, anacetrapib decreases the risk of developing diabetes. If the reduced risk of new-onset diabetes is confirmed in another CETP inhibitor outcome trial, there will be a case for considering the use of the combination of a statin plus a CETP inhibitor in high ASCVD-risk people who are also at increased risk of developing diabetes.

Impact of 3-year changes in lipid parameters and their ratios on incident type 2 diabetes: Tehran lipid and glucose study

BACKGROUND

To examine the impact of changes in all lipid measures including total cholesterol (TC), log-transformed triglycerides (Ln-TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), non-HDL-C, TC/HDL-C and Ln TG/HDL-C, over an approximate 3 year duration, on incident type 2 diabetes (T2DM).

METHODS

A total of 5474 participants, mean age 41.3 years, without prevalent diabetes at baseline or the first follow-up were entered into the study. The association of lipid changes between baseline and the first follow-up i.e., between 1999-2002 and 2002-2005 for those entered in the first phase (n = 4406) and between 2002-2005 and 2005-2008 for participants recruited in the second phase (n = 1068) with incident T2DM over the follow-up period was assessed, using multivariate Cox proportional hazard analysis.

RESULTS

During a median follow-up of 8.9 years after the second lipid measurements, 577 incident cases of T2DM occurred. After adjustment for a wide variety of confounders and body mass index (BMI) change, each 1-SD increase in TC, Ln-TG, HDL-C, LDL-C, non-HDL-C, Ln-TG/HDL-C and TC/HDL-C was associated with 12, 14, 0.86, 12, 16, 15 and 13% risk for T2DM, respectively (all p-values < 0.05). However, after further adjustment for fasting plasma glucose (FPG) change, the risk disappeared for all lipid measures, excluding HDL-C [hazard ratio (HR): 0.84 (0.76-0.93)], Ln-TG/HDL-C [1.14 (1.04-1.25)] and TC/HDL-C [1.12 (1.04-1.21)].

CONCLUSIONS

Three year changes in all lipid parameters, after adjustment for known risk factors of T2DM and BMI changes, were associated with incident T2DM. The independent risk of HDL-C and its ratios remained even after adjustment for FPG changes.

High plasma apolipoprotein B identifies obese subjects who best ameliorate white adipose tissue dysfunction and glucose-induced hyperinsulinemia after a hypocaloric diet

Background

To optimize the prevention of type 2 diabetes (T2D), high-risk obese subjects with the best metabolic recovery after a hypocaloric diet should be targeted. Apolipoprotein B lipoproteins (apoB lipoproteins) induce white adipose tissue (WAT) dysfunction, which in turn promotes postprandial hypertriglyceridemia, insulin resistance (IR), and hyperinsulinemia.

Objective

The aim of this study was to explore whether high plasma apoB, or number of plasma apoB lipoproteins, identifies subjects who best ameliorate WAT dysfunction and related risk factors after a hypocaloric diet.

Design

Fifty-nine men and postmenopausal women [mean ± SD age: 58 ± 6 y; body mass index (kg/m2): 32.6 ± 4.6] completed a prospective study with a 6-mo hypocaloric diet (-500 kcal/d). Glucose-induced insulin secretion (GIIS) and insulin sensitivity (IS) were measured by 1-h intravenous glucose-tolerance test (IVGTT) followed by a 3-h hyperinsulinemic-euglycemic clamp, respectively. Ex vivo gynoid WAT function (i.e., hydrolysis and storage of 3H-triolein-labeled triglyceride-rich lipoproteins) and 6-h postprandial plasma clearance of a 13C-triolein-labeled high-fat meal were measured in a subsample (n = 25).

Results

Postintervention first-phase GIISIVGTT and total C-peptide secretion decreased in both sexes, whereas second-phase and total GIISIVGTT and clamp IS were ameliorated in men (P < 0.05). Baseline plasma apoB was associated with a postintervention increase in WAT function (r = 0.61) and IS (glucose infusion rate divided by steady state insulin (M/Iclamp) r = 0.30) and a decrease in first-phase, second-phase, and total GIISIVGTT (r = -0.30 to -0.35) without sex differences. The association with postintervention amelioration in WAT function and GIISIVGTT was independent of plasma cholesterol (total, LDL, and HDL), sex, and changes in body composition. Subjects with high baseline plasma apoB (1.2 ± 0.2 g/L) showed a significant increase in WAT function (+105%; P = 0.012) and a decrease in total GIISIVGTT (-34%; P ≤ 0.001), whereas sex-matched subjects with low plasma apoB (0.7 ± 0.1 g/L) did not, despite equivalent changes in body composition and energy intake and expenditure.

Conclusions

High plasma apoB identifies obese subjects who best ameliorate WAT dysfunction and glucose-induced hyperinsulinemia, independent of changes in adiposity after consumption of a hypocaloric diet. We propose that subjects with high plasma apoB represent an optimal target group for the primary prevention of T2D by hypocaloric diets. This trial was registered at BioMed Central as ISRCTN14476404.

Endocytosis of lipoproteins

During their metabolism, all lipoproteins undergo endocytosis, either to be degraded intracellularly, for example in hepatocytes or macrophages, or to be re-secreted, for example in the course of transcytosis by endothelial cells. Moreover, there are several examples of internalized lipoproteins sequestered intracellularly, possibly to exert intracellular functions, for example the cytolysis of trypanosoma. Endocytosis and the subsequent intracellular itinerary of lipoproteins hence are key areas for understanding the regulation of plasma lipid levels as well as the biological functions of lipoproteins. Indeed, the identification of the low-density lipoprotein (LDL)-receptor and the unraveling of its transcriptional regulation led to the elucidation of familial hypercholesterolemia as well as to the development of statins, the most successful therapeutics for lowering of cholesterol levels and risk of atherosclerotic cardiovascular diseases. Novel limiting factors of intracellular trafficking of LDL and the LDL receptor continue to be discovered and to provide drug targets such as PCSK9. Surprisingly, the receptors mediating endocytosis of high-density lipoproteins or lipoprotein(a) are still a matter of controversy or even new discovery. Finally, the receptors and mechanisms, which mediate the uptake of lipoproteins into non-degrading intracellular itineraries for re-secretion (transcytosis, retroendocytosis), storage, or execution of intracellular functions, are largely unknown.

The Role of High-Density Lipoproteins in Diabetes and Its Vascular Complications

Almost 600 million people are predicted to have diabetes mellitus (DM) by 2035. Diabetic patients suffer from increased rates of microvascular and macrovascular complications, associated with dyslipidaemia, impaired angiogenic responses to ischaemia, accelerated atherosclerosis, and inflammation. Despite recent treatment advances, many diabetic patients remain refractory to current approaches, highlighting the need for alternative agents. There is emerging evidence that high-density lipoproteins (HDL) are able to rescue diabetes-related vascular complications through diverse mechanisms. Such protective functions of HDL, however, can be rendered dysfunctional within the pathological milieu of DM, triggering the development of vascular complications. HDL-modifying therapies remain controversial as many have had limited benefits on cardiovascular risk, although more recent trials are showing promise. This review will discuss the latest data from epidemiological, clinical, and pre-clinical studies demonstrating various roles for HDL in diabetes and its vascular complications that have the potential to facilitate its successful translation.

Therapy with cholesteryl ester transfer protein (CETP) inhibitors and diabetes risk

BACKGROUND

Cholesteryl ester transfer protein (CETP) inhibitors are a class of drugs that targets the CETP enzyme to significantly increase serum high-density lipoprotein cholesterol (HDL-C) and decrease low-density lipoprotein cholesterol (LDL-C) levels. As HDL-C has potential antidiabetic properties, and the beneficial effects of CETP drugs on glucose homoeostasis have not been sufficiently studied, the aims of this study were: (1) to evaluate the effect of CETP inhibitors on the incidence of diabetes; and (2) to assess the association between CETP inhibitor-induced changes in HDL-C levels and incidence of diabetes.

METHODS

A meta-analysis was performed of randomized controlled clinical trials of CETP inhibitor therapy, either alone or combined with other lipid-lowering drugs, reporting data from new cases of diabetes with a minimum of 6 months of follow-up, after searching the PubMed/MEDLINE, Embase and Cochrane Controlled Trials databases. A fixed-effects meta-regression model was then applied.

RESULTS

Four eligible trials of CETP inhibitors, involving a total of 73,479 patients, were considered for the analyses, including 960 newly diagnosed cases of diabetes in the CTEP inhibitor group vs 1086 in the placebo group. CETP inhibitor therapy was associated with a significant 12% reduction in incidence of diabetes (OR: 0.88, 95% CI: 0.81-0.96; P=0.005). Assessment of the relationship between on-treatment HDL-C and the effect of CETP inhibitors showed a statistically non-significant trend (Z=-1.13, P=0.26).

CONCLUSION

CETP inhibitors reduced the incidence of diabetes. The improvement in glucose metabolism may have been related, at least in part, to the increase in HDL-C concentration.

Hypolipidemic Drugs and Diabetes Mellitus-Mechanisms and Data From Genetic Trials

Clinical trials and meta-analyses have shown that statins can dose dependently increase the incidence of new-onset diabetes mellitus (DM) especially in patients with underlying abnormalities of carbohydrate homeostasis. Mendelian randomization studies support these findings since genetic variants in the gene encoding the target of statins, the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase, are associated with increased incidence of new-onset DM, suggesting that the so-called diabetogenic effect of statins is an "on-target effect" possibly related to their main mechanism of action, that is the increased low-density lipoprotein (LDL) receptor expression. Additionally, Mendelian randomization studies have shown that genetic variants as proxies of other drugs that increase LDL receptor expression (ezetimibe and proprotein convertase subtilisin/kexin type 9 [PCSK9] inhibitors) also increase the risk of new-onset DM. This concept is supported by the fact of decreased DM prevalence in patients with familial hypercholesterolemia who have decreased LDL receptor expression. In contrast, hypolipidemic drugs, such as the cholesteryl ester transfer protein inhibitors, that decrease LDL cholesterol without directly interfering with the LDL receptor expression do not seem to detrimentally affect carbohydrate homeostasis. However, the clinical trials of ezetimibe and PCSK9 inhibitors have not shown an increased DM risk, possibly suggesting that other potential non-well-defined "off-target effects" of hypolipidemic drugs may affect carbohydrate homeostasis. Thus, the long-term effect of hypolipidemic drugs on DM risk depends not only on their final mechanism of hypolipidemic action but also on other "on-target" and "off-target" effects of these drugs.

Elevated Markers of Death Receptor-Activated Apoptosis are Associated with Increased Risk for Development of Diabetes and Cardiovascular Disease

Background

An increased rate of cell death by apoptosis has been implicated in both diabetes and atherosclerosis. Apoptosis can be induced through activation of the death receptors TNF receptor 1 (TNFR-1), TRAIL receptor 2 (TRAILR-2) and Fas. Soluble forms of these receptors are found in plasma. The objective of this study was to determine if soluble death receptors are markers of receptor-activated apoptosis and predict risk for development of diabetes and cardiovascular events.

Methods

Fas ligand was used to induce apoptosis in peripheral blood mononuclear cells and INS-1 pancreatic β-cells and release of TNFR-1, TRAILR-2 and Fas measured by ELISA. Proximity Extension Assay was used to analyze plasma levels of TNFR-1, TRAILR-2 and Fas in baseline samples of 4742 subjects in the Malmö Diet and Cancer Study and related to development of diabetes and cardiovascular events during 19.2 years of follow-up.

Results

Activation of apoptosis by Fas ligand was associated with release of soluble Fas, TNFR-1 and TRAILR-2 in both cell types. Circulating levels of all three receptors were higher in subjects with diabetes and correlated with markers of impaired glucose metabolism in non-diabetic subjects. Among the latter, those in the highest tertile of soluble Fas, TNFR-1 and TRAILR-2 had increased risk for development of diabetes and cardiovascular events. These associations became weaker when adjusting for cardiovascular risk factors in Cox regression models, but remained significant for TRAILR-2 with incident diabetes, cardiovascular mortality, myocardial infarction and ischemic stroke, and for TNFR-1 with myocardial infarction.

Conclusion

The present study demonstrates an association between several cardiovascular risk factors and elevated levels of circulating markers of apoptotic cell death. It also shows that subjects with high levels of these biomarkers have increased risk of diabetes and CVD. This implies that soluble death receptors are markers of β-cell and vascular injury and potentially could be used as surrogate markers of therapeutic efficiency in risk factor interventions.

•Receptor-activated apoptosis is associated with release of soluble death receptors that act as biomarkers of apoptosis •Several cardiovascular risk factors including markers of impaired glucose metabolism associate with elevated plasma levels of death receptors •Subjects with high plasma levels of death receptors have an increased risk of diabetes and cardiovascular disease

Atherosclerosis has been proposed to develop in response to chronic arterial injury caused by cardiovascular risk factors. The present study provides clinical evidence for this hypothesis by demonstrating an association between several cardiovascular risk factors and elevated levels of circulating markers of apoptotic cell death and that subjects with high levels of these biomarkers have increased risk of cardiovascular mortality, MI and stroke. These observations point to the possibility that the plasma level of soluble death receptors can be used as surrogate markers of arterial injury and atherosclerotic disease activity in cardiovascular interventions. Finally, our findings imply that soluble death receptors also may serve as biomarkers of the damage caused by metabolic stress to β-cells and risk for development of type 2 diabetes.

Association between unfavorable lipid profile and glycemic control in patients with type 2 diabetes mellitus

Background:

Recent studies hypothesize that dyslipidemia can predict glycated hemoglobin (HbA1c) and could be important contributing factor to the pathogenesis of type 2 diabetes mellitus (DM2). Therefore, we aimed to evaluate the influence of lipid parameters on long-term glycemic control in DM2.

Materials and Methods:

A total of 275 sedentary DM2 (mean [±standard deviation] age 60.6 [±10.0] years) who volunteered to participate in this cross-sectional study were enrolled. Anthropometric (body weight, body hight, and waist circumference), biochemical parameters (fasting glucose, HbA1c, lipid parameters, creatinine), as well as blood pressure were obtained.

Results:

Total cholesterol (odds ratio [OR] =1.30, 95% confidence interval [CI] [1.02–1.66], P = 0.032), triglycerides (OR = 1.34, 95% CI (1.07–1.67), P = 0.010), and low density lipoprotein cholesterol (OR = 1.42, 95% CI [1.10–1.83], P = 0.006) were the independent predictors of higher HBA1c, and as they increased by 1 mmol/L each, probabilities of higher HBA1c increased by 30%, 34%, and 42%, respectively. Low level of high-density lipoprotein cholesterol (HDL-c) was found to be the independent predictor of higher HBA1c (OR = 0.44, 95% CI [0.20–0.67], P = 0.039), and increase in HDL-c by 1 mmol/L, reduced the probability of higher HBA1c by 56%.

Conclusion:

Unfavorable lipid profile can predict HbA1c level in DM2 patients. Early diagnosis of dyslipidemia, as well as its monitoring and maintaining good lipids control can be used as a preventive measure for optimal long-term glycemic control.

Evaluation of the Pleiotropic Effects of Statins: A Reanalysis of the Randomized Trial Evidence Using Egger Regression-Brief Report

OBJECTIVE

To reanalyze data from recent randomized trials of statins to assess whether the benefits and risks of statins are mediated primarily via their LDL-C (low-density lipoprotein cholesterol) lowering effects or via other mechanisms.

APPROACH AND RESULTS

We adapted Egger regression, a technique frequently used in Mendelian randomization studies to detect genetic pleiotropy, to reanalyze the available randomized control trial data of statin therapy. For cardiovascular end points, each 1 mmol/L change in LDL-C with statin therapy was associated with a hazard ratio of 0.77 (95% confidence interval, 0.71-0.84) with an intercept that was indistinguishable from zero (intercept, -0.0032; [95% confidence interval, -0.090 to 0.084]; P=0.94), indicating no pleiotropy. For incident diabetes mellitus, a 1 mmol/L change in LDL-C with statin therapy was associated with a hazard ratio of 1.07 (95% confidence interval, 0.99-1.16) and an intercept nondistinguishable from zero (intercept, -0.015; [95% confidence interval, -0.30 to 0.27]; P=0.91), again indicating no pleiotropy.

CONCLUSIONS

Our reanalysis of the randomized control trial data using Egger regression adds to the existing evidence that the cardiovascular benefits of statins and their association with incident diabetes mellitus are mediated primarily, if not entirely, via their LDL-C lowering properties rather than by any pleiotropic effects.

Role of apolipoproteins, ABCA1 and LCAT in the biogenesis of normal and aberrant high density lipoproteins

In this review, we focus on the pathway of biogenesis of HDL, the essential role of apoA-I, ATP binding cassette transporter A1 (ABCA1), and lecithin: cholesterol acyltransferase (LCAT) in the formation of plasma HDL; the generation of aberrant forms of HDL containing mutant apoA-I forms and the role of apoA-IV and apoE in the formation of distinct HDL subpopulations. The biogenesis of HDL requires functional interactions of the ABCA1 with apoA-I (and to a lesser extent with apoE and apoA-IV) and subsequent interactions of the nascent HDL species thus formed with LCAT. Mutations in apoA-I, ABCA1 and LCAT either prevent or impair the formation of HDL and may also affect the functionality of the HDL species formed. Emphasis is placed on three categories of apoA-I mutations. The first category describes a unique bio-engineered apoA-I mutation that disrupts interactions between apoA-I and ABCA1 and generates aberrant preβ HDL subpopulations that cannot be converted efficiently to α subpopulations by LCAT. The second category describes natural and bio-engineered apoA-I mutations that generate preβ and small size α4 HDL subpopulations, and are associated with low plasma HDL levels. These phenotypes can be corrected by excess LCAT. The third category describes bio-engineered apoA-I mutations that induce hypertriglyceridemia that can be corrected by excess lipoprotein lipase and also have defective maturation of HDL. The HDL phenotypes described here may serve in the future for diagnosis, prognoses and potential treatment of abnormalities that affect the biogenesis and functionality of HDL.

The association between HDL particle concentration and incident metabolic syndrome in the multi-ethnic Dallas Heart Study

AIMS

Metabolic syndrome (MetS) increases atherosclerotic cardiovascular disease (ASCVD) risk. Low HDL cholesterol (HDL-C) is a diagnostic criterion of MetS and a major ASCVD risk factor. HDL particle concentration (HDL-P) associates with incident ASCVD independent of HDL-C, but its association with incident MetS has not been studied. We hypothesized that HDL-P would be inversely associated with incident metabolic syndrome independent of HDL-C and markers of adiposity and insulin resistance.

MATERIALS AND METHODS

HDL-P was measured by NMR and visceral fat by MRI in participants of the Dallas Heart Study, a probability-based population sample of adults age 30-65. Participants with prevalent MetS, DM, CVD, and any systemic illlness were excluded. Incident MetS as defined by NCEP ATPIII criteria was determined in all participants after median follow-up period of 7.0 years.

RESULTS

Among 1120 participants without DM or MetS at baseline (57% women, 45% Black, mean age 43), 22.8% had incident MetS at follow-up. HDL-P and HDL-C were modestly correlated (r=0.54, p<0.0001). In models adjusted for traditional risk factors and MetS risk factors including visceral fat, HS-CRP, triglyceride to HDL-C ratio, and HOMA-IR, the lowest quartile of HDL-P was associated with a 2-fold increased risk of incident MetS (OR 2.1, 95%CI 1.4-3.1; p=0.0003).

CONCLUSIONS

Low HDL-P is independently associated with incident MetS after adjustment for traditional risk factors, lipid parameters, adiposity, inflammation, and markers of insulin resistance. Further studies are warranted to validate these findings and elucidate the mechanisms underpinning this association.

A Mendelian Randomization Study of Metabolite Profiles, Fasting Glucose, and Type 2 Diabetes

Mendelian randomization (MR) provides us the opportunity to investigate the causal paths of metabolites in type 2 diabetes and glucose homeostasis. We developed and tested an MR approach based on genetic risk scoring for plasma metabolite levels, utilizing a pathway-based sensitivity analysis to control for nonspecific effects. We focused on 124 circulating metabolites that correlate with fasting glucose in the Erasmus Rucphen Family (ERF) study (n = 2,564) and tested the possible causal effect of each metabolite with glucose and type 2 diabetes and vice versa. We detected 14 paths with potential causal effects by MR, following pathway-based sensitivity analysis. Our results suggest that elevated plasma triglycerides might be partially responsible for increased glucose levels and type 2 diabetes risk, which is consistent with previous reports. Additionally, elevated HDL components, i.e., small HDL triglycerides, might have a causal role of elevating glucose levels. In contrast, large (L) and extra large (XL) HDL lipid components, i.e., XL-HDL cholesterol, XL-HDL-free cholesterol, XL-HDL phospholipids, L-HDL cholesterol, and L-HDL-free cholesterol, as well as HDL cholesterol seem to be protective against increasing fasting glucose but not against type 2 diabetes. Finally, we demonstrate that genetic predisposition to type 2 diabetes associates with increased levels of alanine and decreased levels of phosphatidylcholine alkyl-acyl C42:5 and phosphatidylcholine alkyl-acyl C44:4. Our MR results provide novel insight into promising causal paths to and from glucose and type 2 diabetes and underline the value of additional information from high-resolution metabolomics over classic biochemistry.

Relation of four nontraditional lipid profiles to diabetes in rural Chinese H-type hypertension population

Background

Mounting evidence suggested that nontraditional lipid profiles have been recognized as a reliable indicator for unfavorable cardiovascular events. The purpose of this study was to explore the role of nontraditional lipid profiles as potential clinical indices for the assessment of prevalent diabetes in rural Chinese H-type hypertension population.

Methods

During 2012 to 2013, we conducted a large cross-sectional study of 2944 H-type hypertension participants (≥35 years of age) from rural areas in northeast China. Subjects underwent accurate assessment of lipid profiles, fasting plasma glucose (FPG), homocysteine (Hcy) according to standard protocols.

Results

The proportion of diabetes showed a graded and linear increase across the quartiles for all four nontraditional lipid parameters. Nontraditional lipid variables were independent determinants of FPG, and its correlation for TG/HDL-C was strongest, whether potential confounders were adjusted or not. Multivariable logistic regression analysis established that the highest triglycerides (TG)/ high-density lipoprotein cholesterol (HDL-C) quartile manifested the largest ORs of prevalent diabetes (OR: 3.275, 95%CI: 2.109–5.087) compared with the lowest quartile. The fully adjusted ORs (95%CI) were 2.753 (1.783–4.252), 2.178 (1.415–2.351), 1.648 (1.097–2.478) for the top quartile of total cholesterol (TC)/HDL-C, low-density lipoprotein cholesterol (LDL-C)/HDL-C, and non-high-density lipoprotein cholesterol (non-HDL-C), respectively. On the basis of the area under receiver-operating characteristic curve (AUC), TG/HDL-C showed the optimal discriminating power for diabetes (AUC: 0.684, 95% CI: 0.650–0.718).

Conclusions

Nontraditional lipid profiles (TG/HDL-C, TC/HDL-C, LDL-C/HDL-C and non-HDL-C) were all consistently and independently correlated with prevalent diabetes among the H-type hypertension population in rural China. TG/HDL-C was prone to be more profitable in assessing the risk of prevalent diabetes and should be encouraged as an effective clinical tool for monitoring and targeted intervention of diabetes in H-type hypertension adults.

The Role of Inflammation in β-cell Dedifferentiation

Chronic inflammation impairs insulin secretion and sensitivity. β-cell dedifferentiation has recently been proposed as a mechanism underlying β-cell failure in T2D. Yet the effect of inflammation on β-cell identity in T2D has not been studied. Therefore, we investigated whether pro-inflammatory cytokines induce β-cell dedifferentiation and whether anti-inflammatory treatments improve insulin secretion via β-cell redifferentiation. We observed that IL-1β, IL-6 and TNFα promote β-cell dedifferentiation in cultured human and mouse islets, with IL-1β being the most potent one of them. In particular, β-cell identity maintaining transcription factor Foxo1 was downregulated upon IL-1β exposure. In vivo, anti-IL-1β, anti-TNFα or NF-kB inhibiting sodium salicylate treatment improved insulin secretion of isolated islets. However, only TNFα antagonism partially prevented the loss of β-cell identity gene expression. Finally, the combination of IL-1β and TNFα antagonism improved insulin secretion of ex vivo isolated islets in a synergistic manner. Thus, while inflammation triggered β-cell dedifferentiation and dysfunction in vitro, this mechanism seems to be only partly responsible for the observed in vivo improvements in insulin secretion.

Effect of LDL cholesterol, statins and presence of mutations on the prevalence of type 2 diabetes in heterozygous familial hypercholesterolemia

Patients with heterozygous familial hypercholesterolemia (HeFH) have been reported to be less vulnerable to type 2 diabetes mellitus (T2DM), although the mechanism is unknown. The aims of the present study were to assess the effects of low density lipoprotein (LDL) cholesterol concentration and the presence of FH-causing mutations on T2DM prevalence in HeFH. Data were collected from the Dyslipidemia Registry of the Spanish Arteriosclerosis Society. Inclusion criteria were definite or probable HeFH in patients aged ≥18 years. T2DM prevalence in HeFH patients was compared with data of the general population. 1732 patients were included. The prevalence of T2DM was lower in patients with HeFH compared with the general population (5.94% vs 9.44%; OR: 0.606, 95% CI 0.486-0.755, p < 0.001). Risk factors for developing T2DM were male sex, age, body mass index, hypertension, baseline triglyceride levels and years on statin therapy. The prevalence of T2DM in HeFH patients was 40% lower than that observed in the general population. Gene mutations and LDL cholesterol concentrations were not risk factors associated with the prevalence of T2DM in patients with HeFH. The prevalence of T2DM in patients with HeFH was 40% lower than in the general population matched for age and sex.

Statins and New-Onset Diabetes Mellitus: LDL Receptor May Provide a Key Link

Numerous studies have noted that populations treated with statins have increased risk for new-onset diabetes mellitus; however, the underlying molecular mechanisms are not fully understood. Interestingly, familial hypercholesterolemia (FH) patients with mutations in the low-density lipoprotein receptor (LDLR) gene are protected against diabetes mellitus (DM), despite these patients being subjected to long-term statin therapy. Since the common pathway between FH and statin therapy is LDLR-mediated cellular cholesterol uptake, the arising question is whether the LDLR plays an important role in the diabetogenic effect of statins. Indeed, given that statins can regulate the LDLR expression in liver and peripheral tissue, there is a possible mechanism that the increased LDLR causes cellular cholesterol accumulation and dysfunction in pancreatic islets, explaining why statins fail to increase the risk of DM in FH patients. In this paper, with regarded to recent literatures, we highlight the role of LDLR in the pathophysiology of cholesterol-induced pancreatic islets dysfunction, which may provide the key link between statins treatment and the increased risk of new-onset diabetes mellitus.

Can LDL cholesterol be too low? Possible risks of extremely low levels

Following the continuous accumulation of evidence supporting the beneficial role of reducing low-density lipoprotein cholesterol (LDL-C) levels in the treatment and prevention of atherosclerotic cardiovascular disease and its complications, therapeutic possibilities now exist to lower LDL-C to very low levels, similar to or even lower than those seen in newborns and nonhuman species. In addition to the important task of evaluating potential side effects of such treatments, the question arises whether extremely low LDL-C levels per se may provoke adverse effects in humans. In this review, we summarize information from studies of human cellular and organ physiology, phenotypic characterization of rare genetic diseases of lipid metabolism, and experience from clinical trials. Specifically, we emphasize the importance of the robustness of the regulatory systems that maintain balanced fluxes and levels of cholesterol at both cellular and organismal levels. Even at extremely low LDL-C levels, critical capacities of steroid hormone and bile acid production are preserved, and the presence of a cholesterol blood-brain barrier protects cells in the central nervous system. Apparent relationships sometimes reported between less pronounced low LDL-C levels and disease states such as cancer, depression, infectious disease and others can generally be explained as secondary phenomena. Drug-related side effects including an increased propensity for development of type 2 diabetes occur during statin treatment, whilst further evaluation of more potent LDL-lowering treatments such as PCSK9 inhibitors is needed. Experience from the recently reported and ongoing large event-driven trials are of great interest, and further evaluation including careful analysis of cognitive functions will be important.

Low apoA-I is associated with insulin resistance in patients with impaired glucose tolerance: a cross-sectional study

Background

Low apolipoprotein A-I (apoA-I) is an independent risk factor for atherosclerotic cardiovascular diseases. Insulin resistance predicts the progression of abnormal glucose metabolism, which is the main cause of atherosclerotic cardiovascular disease. In this study, we assessed the potential association between apoA-I levels and insulin resistance in patients with impaired glucose tolerance (IGT) and the possible link between apoA-I and IGT.

Methods

This study evaluated a cross-sectional study of 108 participants with impaired glucose tolerance (IGT group) and 84 controls (control group). ApoA-I and clinical characteristics were measured, and a homeostasis model assessment of insulin resistance (HOMA-IR) was calculated.

Results

The IGT group exhibited significantly lower apoA-I and higher HOMA-IR levels than the control group (apoA-I: 1.37 ± 0.36 vs 1.57 ± 0.39 g/L; HOMA-IR: 4.21 ± 1.56 vs 2.15 ± 0.99; P < 0.001 for both). ApoA-I was negatively correlated with HOMA-IR in both the IGT and control groups (IGT group: r = −0.269, P = 0.005; control group: r = −0.262, P = 0.016). Multiple stepwise regression analysis showed that low apoA-I levels (β = −1.470, P = 0.002) were independently correlated with high HOMA-IR levels in the IGT group. Moreover, logistic regression analysis identified that low apoA-I was an independent influencing factor for IGT (β = −1.170, OR = 0.310, P = 0.007).

Conclusions

ApoA-I is inversely associated with insulin resistance in patients with impaired glucose tolerance, and low apoA-I is an independent risk factor for impaired glucose tolerance. These results indicate that apoA-I plays an important role in regulating insulin sensitivity and glucose metabolism in patients with IGT.